Surgical instrument with articulation assembly

ABSTRACT

A surgical instrument includes an articulation assembly having a threaded rod, a first nut, a second nut, a first articulation rod, and a second articulation rod. The threaded rod includes a body, a first thread encircling a proximal portion of the body in a first direction, and a second thread spaced from the first thread and encircling a distal portion of the body in a second, opposite direction. Rotation of the threaded rod in a first direction relative to the elongated portion causes the first nut to move distally relative to the threaded rod. Rotation of the threaded rod in the first direction relative to the elongated portion causes the second nut to move proximally relative to the threaded rod. The first articulation rod is coupled to the first nut and the end effector, and the second articulation rod is coupled to the second nut and the end effector.

FIELD

The present disclosure relates to a surgical instrument including an articulation assembly. More particularly, the present disclosure relates to a surgical instrument having a robust articulation assembly enabling a controlled articulation of an end effector of the surgical instrument.

BACKGROUND

Various types of surgical instruments used to endoscopically treat tissue are known in the art, and are commonly used, for example, for closure of tissue or organs in transection, resection, anastomoses, for occlusion of organs in thoracic and abdominal procedures, and for electrosurgically fusing or sealing tissue.

One example of such a surgical instrument is a surgical stapling instrument. Typically, surgical stapling instruments include an end effector having an anvil assembly and a cartridge assembly for supporting an array of surgical staples, an approximation mechanism for approximating the cartridge and anvil assemblies, a rotation assembly for rotating the cartridge and anvil assemblies about an axis, and a firing mechanism for ejecting the surgical staples from the cartridge assembly.

During laparoscopic or endoscopic surgical procedures, access to a surgical site is achieved through a small incision or through a narrow cannula inserted through a small entrance wound in a patient. Because of limited area available to access the surgical site, many endoscopic instruments include mechanisms for articulating the end effector of the instrument in relation to a body portion of the instrument to improve access to tissue to be treated.

It would be beneficial to provide an improved surgical instrument having a robust articulation assembly that would facilitate a controlled articulation of the end effector to further improve access to target tissue.

SUMMARY

The present disclosure relates to a surgical instrument including a handle assembly, an elongated portion, an end effector, and an articulation assembly. The elongated portion extends distally from the handle assembly and defines a first longitudinal axis. The end effector is disposed adjacent a distal end of the elongated portion and defines a second longitudinal axis. The articulation assembly is disposed in mechanical cooperation with the end effector and is configured to cause the end effector to move between a first position where the second longitudinal axis is aligned with the first longitudinal axis and a second position where the second longitudinal axis is disposed at an angle to the first longitudinal axis. The articulation assembly includes a threaded rod, a first nut, a second nut, a first articulation rod, and a second articulation rod. The threaded rod includes a body, a first thread encircling a proximal portion of the body in a first direction, and a second thread spaced from the first thread and encircling a distal portion of the body in a second direction. The first direction is opposite the second direction. The first nut is mechanically engaged with the first thread such that rotation of the threaded rod in a first direction relative to the elongated portion causes the first nut to move distally relative to the threaded rod. The second nut is mechanically engaged with the second thread such that rotation of the threaded rod in the first direction relative to the elongated portion causes the second nut to move proximally relative to the threaded rod. The first articulation rod is coupled to the first nut and to the end effector, and the second articulation rod is coupled to the second nut and to the end effector.

In aspects, an entirety of the first thread may be disposed proximally of the second thread.

In disclosed aspects, the surgical instrument may include an actuation mechanism disposed in mechanical cooperation with the handle assembly and with the articulation assembly. The surgical instrument may also include a driver disposed in mechanical cooperation with the articulation assembly and in mechanical cooperation with the actuation mechanism. The driver may be rotatable about the longitudinal axis relative to the elongated portion. In aspects, the driver may be disposed in mechanical cooperation with the threaded rod, and the driver may be rotationally fixed with respect to the threaded rod.

In aspects, the first nut may be translatable proximally and translatable distally relative to the elongated portion, and the second nut may be translatable proximally and translatable distally relative to the elongated portion.

In further aspects, the first articulation rod may be longitudinally fixed to the first nut, and the second articulation rod may be longitudinally fixed to the second nut.

In disclosed aspects, rotation of the threaded rod in the first direction about the longitudinal axis relative to the elongated portion may cause the first articulation rod to move distally relative to the elongated portion and may cause the second articulation rod to move proximally relative to the elongated portion. In aspects, rotation of the threaded rod in a second direction about the longitudinal axis relative to the elongated portion may cause the first articulation rod to move proximally relative to the elongated portion and may cause the second articulation rod to move distally relative to the elongated portion.

In yet other aspects, the first nut and the second nut may be rotationally fixed relative to the elongated portion.

In disclosed aspects, the articulation assembly may further include a proximal stop disposed on the threaded rod proximally of the first nut, a distal stop disposed on the dal threaded rod distally of the second nut, and a middle stop disposed on the threaded rod distally of the first nut and proximally of the second nut.

The present disclosure also relates to an articulation assembly for use with a surgical device including a threaded rod, a proximal nut, a distal nut, a first articulation rod, and a second articulation rod. The threaded rod includes a body, a first thread encircling a proximal portion of the body in a first direction, and a second thread spaced from the first thread and encircling a distal portion of the body in a second direction. The first direction is opposite the second direction. The proximal nut encircles the body of the threaded rod and engages with the first thread of the threaded rod. The distal nut encircles the body of the threaded rod and engages with the second thread of the threaded rod. The first articulation rod is coupled to the proximal nut and is disposed on a first lateral side of the threaded rod. The second articulation rod is coupled to the distal nut and is disposed on a second lateral side of the threaded rod. Rotation of the threaded rod in a first direction relative to the proximal nut causes the proximal nut and the first articulation rod to move distally relative to the threaded rod, and causes the distal nut and the second articulation rod to move proximally relative to the threaded rod.

In aspects, an entirety of the first thread may be disposed proximally of an entirety of the second thread.

In disclosed aspects, rotation of the threaded rod in a second direction relative to the proximal nut may cause the proximal nut and the first articulation rod to move proximally relative to the threaded rod, and may cause the distal nut and the second articulation rod to move distally relative to the threaded rod.

In aspects, the articulation assembly may also include a proximal stop disposed on the threaded rod proximally of the proximal nut, and a distal stop disposed on the threaded rod distally of the distal nut.

The present disclosure also relates to a method of articulating an end effector of a surgical instrument. The method includes rotating a threaded rod having a right-hand thread on a first portion thereof, and having a left-hand thread on a second portion thereof, where the right-hand thread is spaced apart from the left-hand thread, translating a first nut proximally. The method also includes translating a second nut distally, translating a first articulation rod proximally, and translating a second articulation rod distally. Translating the first nut proximally and translating the second nut distally occur simultaneously.

In disclosed aspects, translating the first articulation rod proximally and translating the second articulation rod distally may occur simultaneously. In aspects, translating the first nut proximally and translating the first articulation rod proximally may occur simultaneously.

In yet other aspects, the threaded rod may define a first longitudinal axis, the end effector may define a second longitudinal axis, and the method may further include moving the end effector from a first position wherein the first longitudinal axis is aligned with the second longitudinal axis, to a second position where the second longitudinal axis is disposed at about 90° relative to the first longitudinal axis.

DESCRIPTION OF THE DRAWINGS

Various aspects of the present disclosure are illustrated herein with reference to the accompanying drawings, wherein:

FIG. 1 is a perspective view of a surgical instrument in accordance with an aspect of the present disclosure;

FIG. 2 is a perspective view of the area of detail indicated in FIG. 1 illustrating an articulation assembly of the surgical instrument;

FIG. 3 is a perspective view of the area of detail indicated in FIG. 2 ;

FIG. 4 is an exploded view of the articulation assembly of FIG. 2 ;

FIG. 5 is a plan view of a portion of the articulation assembly of FIG. 2 corresponding to an end effector of the surgical instrument being in a non-articulated position;

FIG. 6 is a radial cross-sectional view of the surgical instrument taken along section line 6-6 in FIG. 5 ;

FIG. 7 is a plan view of a portion of the articulation assembly of FIG. 2 corresponding to the end effector of the surgical instrument being in a first articulated position;

FIG. 8 is a plan view of portions of the articulation assembly and the end effector of the surgical instrument of FIG. 2 in the first articulated position;

FIG. 9 is a plan view of a portion of the articulation assembly of FIG. 2 corresponding to the end effector of the surgical instrument being in a second articulated position; and

FIG. 10 is a plan view of portions of the articulation assembly and the end effector of the surgical instrument of FIG. 2 in the second articulated position.

DETAILED DESCRIPTION

Aspects of the presently disclosed surgical instrument will now be described in detail with reference to the drawings wherein like numerals designate identical or corresponding elements in each of the several views. As is common in the art, the term “proximal” refers to that part or component closer to the user or operator, i.e. surgeon or physician, while the term “distal” refers to that part or component farther away from the user.

A surgical instrument of the present disclosure is indicated as reference numeral 100 in FIG. 1 . Generally, the surgical instrument 100 includes a handle assembly 110, an elongated portion 120 extending distally from handle assembly 110 and defining a longitudinal axis “A-A,” a loading unit 200 disposed adjacent a distal end of elongated portion 120, and an articulation assembly 500 (FIGS. 2-7 and 9 ). While FIG. 1 illustrates surgical instrument 100 including a handle assembly 110 having a trigger 112, various types of handles can be used such as, for example, a pivotable handle, powered, motor-driven, hydraulic, ratcheting, etc. As used herein, “handle assembly” encompasses all types of handle assemblies. Additionally, a robotic surgical system may be used in connection with the aspects of the present disclosure.

The loading unit 200 may be releasably attachable to the elongated portion 120 of the surgical instrument 100, e.g., to allow the surgical instrument 100 to have greater versatility. This arrangement allows the clinician to select a particular loading unit 200 for a given procedure. As used herein, “loading unit” encompasses both single use loading units (“SULU”) and disposable loading units (“DLU”). Additionally or alternatively, the surgical instrument 100 may have a cartridge that is removable and replaceable in the reusable jaws of the surgical instrument.

Examples of loading units for use with a surgical stapling instrument are disclosed in commonly-owned U.S. Pat. No. 5,752,644 to Bolanos et al., the entire contents of which are hereby incorporated by reference herein. Further details of an endoscopic surgical stapling instrument are described in detail in commonly-owned U.S. Pat. No. 6,953,139 to Milliman et al., the entire contents of which are hereby incorporated by reference herein.

With reference to FIG. 2 , the loading unit 200 of the present disclosure is shown. The loading unit 200 includes a proximal body portion 210, and a tool assembly or end effector 220 defining an axis “B-B” and including a pair of jaw members (i.e., an anvil assembly 300 and a cartridge assembly 400). In aspects, the proximal body portion 210 may be configured to removably attach to the elongated portion 120 of surgical instrument 100.

In the surgical instrument 100 in accordance with disclosed aspects, actuation of the trigger 112 (and/or at least one additional actuation mechanism) causes movement of at least one jaw member towards the other jaw member, distal movement of a firing rod to deploy fasteners from the cartridge assembly 400, and/or distal movement of a knife to sever tissue.

Additionally, actuation of an articulation lever or controls 114 a, 114 b (FIG. 1 ; collectively “articulation control 114”) engages the articulation assembly 500 and causes the end effector 220 to move from a first position (FIG. 1 ) where the axis “B-B” defined by the end effector 220 is aligned with the longitudinal axis “A-A,” to a second position (FIG. 10 ) where the axis “B-B” is disposed at an angle (e.g. up to about 90°) relative to the longitudinal axis “A-A.”

With reference to FIGS. 3-7 and 9 , the articulation assembly 500 includes a driver 510, a threaded rod 520, a proximal stop 530, a middle stop 540, a distal stop 550, a proximal nut 560, a distal nut 570, a first articulation rod 580, and a second articulation rod 590. Additionally, and with particular reference to FIG. 4 , the surgical instrument 100 includes a pivot assembly 600, which interconnects the articulation assembly 500 with the anvil assembly 300 and the cartridge assembly 400. The pivot assembly 600 includes a first pivot link 610 pinned to the first articulation rod 580 by a first pin 612, and pinned to a proximal end of the anvil assembly 300 and the cartridge assembly 400 by a second pin 614. The pivot assembly 600 also includes a second pivot link 620 pinned to the second articulation rod 590 by a third pin 622, and pinned to a proximal end of the anvil assembly 300 and the cartridge assembly 400 by a fourth pin 624.

With particular reference to FIGS. 3 and 4 , further details of the articulation assembly 500 of the surgical instrument 100 are shown. The driver 510 is rotatable about the longitudinal axis “A-A” in response to actuation of the articulation control 114 (FIG. 1 ). The threaded rod 520 is disposed adjacent a distal end of the driver 510 and is rotationally fixed relative to the driver 510. The threaded rod 520 includes a body 521, a first thread or series of threads 522 (e.g., right-hand threads) encircling the body 521 in a first direction (e.g., clockwise) and a second thread series of threads 524 (e.g., left-hand threads) encircling the body 521 in a second, opposite direction (e.g., counter-clockwise).

The first thread 522 is disposed on a proximal portion 520 a of the threaded rod 520, and the second thread 524 is disposed on a distal portion 520 b of the threaded rod 520. As shown, the first thread 522 is longitudinally spaced from the second thread 524 such that the first thread 522 and the second thread 524 do not overlap each other. In disclosed aspects, the longitudinal length of the first thread 522 is equal to or approximately equal to the longitudinal length of the second thread 524. A mid-portion 520 c (FIG. 4 ) of the threaded rod 520 may include no threads, or alternatively, the first threads 522 may meet the second threads 524 at the mid-portion 520 c of the threaded rod 520.

With continued reference to FIGS. 3 and 4 , the proximal stop 530 encircles a proximal end of the threaded rod 520 (e.g., proximally adjacent or in contact with the first thread 522) and is rotationally and longitudinally fixed relative to the threaded rod 520. The distal stop 550 encircles a distal end of the threaded rod 520 (e.g., distally adjacent or in contact with the second thread 524) and is rotationally and longitudinally fixed relative to the threaded rod 520. The middle stop 540 encircles the mid-portion 520 c of the threaded rod 520 and is positioned between (or in contact with) the first thread 522 and the second thread 524, and between the proximal stop 530 and the distal stop 550.

The proximal nut 560 encircles part of the proximal portion 520 a of the threaded rod 520 and is positioned between the proximal stop 530 and the middle stop 540. More particularly, the proximal nut 560 defines an aperture 562, and the wall defining the aperture 562 includes a thread 564 (e.g., right-hand thread; FIG. 4 ). The thread 564 of the proximal nut 560 is configured to engage or mesh with the first thread 522 of the threaded rod 520 such that rotation of the threaded rod 520 in a first direction (e.g., in the general direction of arrow “C” in FIG. 9 ) causes the proximal nut 560 to move in a first longitudinal direction (e.g., in the general direction of arrow “D” in FIG. 9 —distally), and rotation of the threaded rod 520 in a second direction (e.g., in the general direction of arrow “E” in FIG. 7 ) causes the proximal nut 560 to move in a second longitudinal direction (e.g., in the general direction of arrow “P” in FIG. 7 —proximally).

The distal nut 570 encircles part of the distal portion 520 b of the threaded rod 520 and is positioned between the distal stop 550 and the middle stop 540. More particularly, the distal nut 570 defines an aperture 572, and the wall defining the aperture 572 includes a thread 574 (e.g., left-hand thread; FIG. 4 ). The thread 574 of the distal nut 570 is configured to engage or mesh with the second thread 524 of the threaded rod 520 such that rotation of the threaded rod 520 in the first direction (e.g., in the general direction of arrow “C” in FIG. 9 ) causes the distal nut 570 to move in the second longitudinal direction (e.g., in the general direction of arrow “P” in FIG. 9 —proximally), and rotation of the threaded rod 520 in the second direction (e.g., in the general direction of arrow “E” in FIG. 7 ) causes the distal nut 570 to move in the longitudinal direction (e.g., in the general direction of arrow “D” in FIG. 7 —distally).

That is, rotation of the threaded rod 520 in the first direction (e.g., in the general direction of arrow “C” in FIG. 9 ) causes the proximal nut 560 to move distally and simultaneously causes the distal nut 570 to move proximally. Rotation of the threaded rod 520 in the second direction (e.g., in the general direction of arrow “E” in FIG. 7 ) causes the proximal nut 560 to move proximally and simultaneously causes the distal nut 570 to move distally. Moreover, rotation of the threaded rod 520 causes the proximal nut 560 and the distal nut 570 to move in opposite directions from each other, simultaneously.

Referring now to FIGS. 3, 5, and 7 , the proximal stop 530 is positioned with respect to the threaded rod 520 such that the proximal stop 530 limits the amount of proximal movement of the proximal nut 560 relative to the threaded rod 520. The middle stop 540 is positioned with respect to the threaded rod 520 such that the middle stop 540 limits the amount of distal movement of the proximal nut 560 relative to the threaded rod 520, and limits the amount of proximal movement of the distal nut 570 relative to the threaded rod 520. The distal stop 550 is positioned with respect to the threaded rod 520 such that the distal stop 550 limits the amount of distal movement of the distal nut 570 relative to the threaded rod 520.

With reference to FIG. 6 , a radial cross-section of a portion of the articulation assembly 500 and the elongated portion 120 is shown. The elongated portion 120 includes an outer wall 122 and an inner body 124. The inner body 124 defines an opening 126 dimensioned to accommodate the proximal nut 560, the distal nut 570 (not shown in FIG. 6 ), the first articulation rod 580, and the second articulation rod 590 (not shown in FIG. 6 ). The shape of the opening 126 of the elongated portion 120 ensures that the proximal nut 560, the distal nut 570, the first articulation rod 580, and the second articulation rod 590 are fixed from rotation about the longitudinal axis “A-A” (FIG. 1 ) relative to the elongated portion 120. Accordingly, rotation of the threaded rod 520 relative to the elongated portion 120 results longitudinal translation (and no rotation) of the proximal nut 560, the distal nut 570, the first articulation rod 580, and the second articulation rod 590 relative to the elongated portion 120.

Referring to FIGS. 2, 3, 5, and 7 , the proximal nut 560 is mechanically coupled to the first articulation rod 580, and the distal nut 570 is mechanically coupled to the second articulation rod 590. More particularly, with particular reference to FIG. 5 , the first articulation rod 580 is affixed to a first lateral side 562 of the proximal nut 560, and the second articulation rod 590 is affixed to a second lateral side 572 of the distal nut 570. The first lateral side 562 of the proximal nut 560 and the second lateral side 572 of the distal nut 570 are on opposite sides of the longitudinal axis “A-A.” Accordingly, longitudinal movement of the proximal nut 560 causes a corresponding longitudinal movement of the first articulation rod 580 on a first side of the longitudinal axis “A-A,” and longitudinal movement of the distal nut 570 causes a corresponding longitudinal movement of the second articulation rod 590 on a second side of the longitudinal axis “A-A.”

Moreover, rotation of the threaded rod 520 in the first direction (e.g., in the general direction of arrow “C” in FIG. 9 ) causes the proximal nut 560 and the first articulation rod 580 to move distally, and simultaneously causes the distal nut 570 and the second articulation rod 590 to move proximally. Rotation of the threaded rod 520 in the second direction (e.g., in the general direction of arrow “E” in FIG. 7 ) causes the proximal nut 560 and the first articulation rod 580 to move proximally, and simultaneously causes the distal nut 570 and the second articulation rod 590 to move distally.

Referring now to FIGS. 4, 8, and 10 , engagement between the articulation assembly 500 and the pivot assembly 600 is shown. As noted above, the first articulation rod 580 is pivotably coupled to the first pivot link 610 by a first pin 612, and the second articulation rod 590 is pivotably coupled to the second pivot link 620 by a third pin 622. The first pivot link 610 is pivotably coupled to the proximal end of the anvil assembly 300 and the cartridge assembly 400 by a second pin 614, and the second pivot link 620 is pivotably coupled to the anvil assembly 300 and the cartridge assembly 400 by a fourth pin 624. Accordingly, when the first articulation rod 580 is moved proximally and when the second articulation rod 590 is moved distally (which, as discussed above, occur simultaneously), the end effector 220 is moved or articulated in the general direction of arrow “R” (FIG. 8 ). Likewise, when the first articulation rod 580 is moved distally and when the second articulation rod 590 is moved proximally (which, as discussed above, occur simultaneously), the end effector 220 is moved or articulated in the general direction of arrow “L” (FIG. 10 ).

Thus, the end effector 220 is being simultaneously pushed and pulled in opposite directions. More particularly, when one lateral side of the end effector 220 is being pushed, the opposite lateral side of the end effector 220 is being pulled, and vice versa. Therefore, a mechanical advantage exists versus an articulation assembly including a single articulation rod, for instance, which is only able to push or pull the end effector, instead of being able to push and pull the end effector.

While the above description contains many specifics, these specifics should not be construed as limitations on the scope of the present disclosure, but merely as illustrations of various aspects thereof. Therefore, the above description should not be construed as limiting, but merely as exemplifications of various aspects. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto. 

What is claimed is:
 1. A surgical instrument, comprising: a handle assembly; an elongated portion extending distally from the handle assembly and defining a first longitudinal axis, wherein a proximal end of the elongated portion is positioned distally of a distal end of the handle assembly, the elongated portion includes a constant diameter along its entire length; an end effector disposed adjacent a distal end of the elongated portion and defining a second longitudinal axis; and an articulation assembly disposed in mechanical cooperation with the end effector and configured to cause the end effector to move between a first position where the second longitudinal axis is aligned with the first longitudinal axis and a second position where the second longitudinal axis is disposed at an angle to the first longitudinal axis, an entirety of the articulation assembly disposed within the elongated portion, the articulation assembly includes: a threaded rod including a body, the body disposed coaxially with the first longitudinal axis, a first thread encircling a proximal portion of the body in a first direction, and a second thread spaced from the first thread and encircling a distal portion of the body in a second direction, the first direction is opposite the second direction; a first nut mechanically engaged with the first thread such that rotation of the threaded rod in a first direction relative to the elongated portion causes the first nut to move distally relative to the elongated portion; a second nut mechanically engaged with the second thread such that rotation of the threaded rod in the first direction relative to the elongated portion causes the second nut to move proximally relative to the elongated portion; a first articulation rod coupled to the first nut and to the end effector, the first articulation rod being fixed from rotation about the first longitudinal axis relative to the elongated portion; and a second articulation rod coupled to the second nut and to the end effector.
 2. The surgical instrument according to claim 1, wherein an entirety of the first thread is disposed proximally of the second thread.
 3. The surgical instrument according to claim 1, further including an actuation mechanism disposed in mechanical cooperation with the handle assembly and with the articulation assembly.
 4. The surgical instrument according to claim 3, further including a driver disposed in mechanical cooperation with the articulation assembly and in mechanical cooperation with the actuation mechanism, the driver rotatable about the first longitudinal axis relative to the elongated portion.
 5. The surgical instrument according to claim 4, wherein the driver is disposed in mechanical cooperation with the threaded rod, the driver is rotationally fixed with respect to the threaded rod.
 6. The surgical instrument according to claim 1, wherein the first nut is translatable proximally and translatable distally relative to the elongated portion, and wherein the second nut is translatable proximally and translatable distally relative to the elongated portion.
 7. The surgical instrument according to claim 1, wherein the first articulation rod is longitudinally fixed to the first nut, and wherein the second articulation rod is longitudinally fixed to the second nut.
 8. The surgical instrument according to claim 1, wherein rotation of the threaded rod in the first direction about the first longitudinal axis relative to the elongated portion causes the first articulation rod to move distally relative to the elongated portion and causes the second articulation rod to move proximally relative to the elongated portion.
 9. The surgical instrument according to claim 8, wherein rotation of the threaded rod in a second direction about the first longitudinal axis relative to the elongated portion causes the first articulation rod to move proximally relative to the elongated portion and causes the second articulation rod to move distally relative to the elongated portion.
 10. The surgical instrument according to claim 1, wherein the first nut and the second nut are rotationally fixed relative to the elongated portion.
 11. The surgical instrument according to claim 1, wherein the articulation assembly further includes a proximal stop disposed on the threaded rod proximally of the first nut, and a distal stop disposed on the threaded rod distally of the second nut.
 12. The surgical instrument according to claim 11, wherein the articulation assembly further includes a middle stop disposed on the threaded rod distally of the first nut and proximally of the second nut.
 13. The surgical instrument according to claim 1, wherein the elongated portion includes an inner body defining an opening configured to accommodate the first nut and the second nut in non-rotatable engagement with the elongated portion.
 14. The surgical instrument according to claim 13, wherein the opening defined by the inner body of the elongated portion includes a first wall configured to engage a first surface of the first articulation rod, a second wall extending at an angle from the first wall and configured to engage a second surface of the first articulation rod, a third wall extending at an angle from the second wall and configured to engage a first surface of the first nut, a fourth wall extending at an angle from the third wall and configured to engage a second surface of the first nut, a fifth wall extending at an angle from the fourth wall and configured to engage a first surface of the second articulation rod, and a sixth wall extending at an angle from the fifth wall and configured to engage a second surface of the second articulation rod. 